As shown in FIG. 6, a conventional plate type heat exchanger has a plurality of tube units each of which is formed by a couple of plates 101 in which is formed a cup shape portion 401, a plurality of corrugated fins 203 being provided between adjacent pair of the tube units. Plates 101 are connected to each other at a connecting portion 101a by brazing, and the corrugated fin 203 and the plate 101 are connected each other. The tube unit has an enlarged portion 101b elongating outwardly from the connecting portion 101a so that a cup shaped draining space portion 401 is formed within the elongating portion 101b, the connecting portion 101a and the side surface of the fin 203.
Since the heat exchanger is used as the evaporator of an automotive air conditioner, the moisture within the atmosphere is condensed on the outer surface of the plate 101 and the corrugated fin 203. The condensed water flows toward the down flow of the air passing through the heat exchanger, so that the condensed water is introduced into the draining space 401 which locates at the down flow of the air. The hatched portion in FIGS. 6 and 7 indicates the condensed water. The present inventors have observed that while some condensed water is introduced into the draining space 401 much remains at the end portion of the corrugated fins 203. The present inventors' found that the condensed water remains at the end portion of the corrugated fin 203 because of the surface tension caused at the touching portion between the elongating portion 101b and the corrugated fin 203. The droplets remaining on the corrugated fin 203 may disperse toward the passenger's compartment of the automobile, and it, of course, causes serious disadvantages.
In order to solve the disadvantages of the dispersion of the condensed water, it is necessary to eliminate the surface tension which makes the condensed water remain at the end portion of the fin 203.
FIG. 8 shows a type of the heat exchanger which the present inventors had made in an attempt to overcome the problem. The heat exchanger shown in FIG. 8 has no elongating portion so that the connecting portion 101d is apart from the corrugated fin 203. According to the present inventors' study, the heat exchanger shown in FIG. 8 cannot solve the problem of dispersion of the condensed water. Since the heat exchanger shown in FIG. 8 has no elongating portion, the draining space 401x between the connecting portion 101d and the corrugate fin 203 cannot work as effectively as that of the heat exchanger shown in FIG. 6. Therefore, the condensed water generated on the corrugated fin 203 cannot drain downwardly through the draining space 401x but disperses toward the passenger's compartment. Furthermore, the tube unit shown in FIG. 8 cannot have an effective sealing efficiency since the coolant within the tube unit may leak through the connecting portion 101d.
Since the plates 101 are connected to each other by brazing, and the brazing material is cladded on the surface of the plate 101, a shortage of the total amount of brazing material at the connecting portion 101d may occur when the total area of the connecting portion 101d is too large.